Theorem 3.10 (cf. [1]}, [2]}, [3]}) 

There is a constant \(\gamma \)  such that for \(A \in \sigma (\mathcal {A}_G^l)\) , \(B \in \mathcal {B}\)  and for \(n \in \mathbb {N}\)
\(\left| \lambda (A \cap T_G^{-n-l} B) - \lambda (A) \mu _G(B) \right| = \lambda (A) \, \mu _G(B) \, O(e^{- \gamma n}).\) 

